In the drilling of oil and gas wells as well as other downhole activities, it is common to use a downhole system which provides a percussive or hammer effect to the drill string to increase drilling rate. In typical drilling operations, a drilling fluid or mud is pumped from the surface, through the drill string and exits through nozzles in the drill bit. The fluid flow from the nozzles assists in dislodging and cleaning cuttings from the bottom of the borehole as well as carrying the cuttings back to the surface. It is also common in addition to using the pulsing apparatus to incorporate a pressure-responsive tool in the drill string which expands or retracts in response to the varying fluid pressure pulses created by operation of the pulsing apparatus. This expansion/retraction motion provides desired pulsed mud jets to assist mechanical action of a drill bit. The pulsed mud jets have significant advantages over continuous streams jets. They exert alternating loads onto the rock formation to produce a water hammer effect and high the tensile stress on the formation, which will weaken the formation through the reflection of stress waves, prior to mechanical action of the drill bit, resulting in faster penetration rates. Such an apparatus may be in the form of a shock sub or tool and, may be provided above or below the pulsing apparatus or in certain cases can form part of a pulsing apparatus.
Various types of pulsing apparatuses have been employed in order to provide vibration. Some such pulsing apparatuses typically employ reciprocating impact elements that move back and forth along the axis of the pipe string to induce vibration in the pipe string. Other such pulsing apparatuses employ the use of eccentrically weighted rotating masses, eccentric shafts or rods, or rotatable impact elements that rotate about the longitudinal axis of the drill or pipe string to strike an impact anvil in order to apply a rotational or torsional vibration to the pipe string.
Still other types of pulsing apparatuses utilize Moineau power sections that are generally used in downhole mud motors or pumps. Moineau power sections typically utilize rubber or rubber-like elastomers as seals which are negatively affected by elevated wellbore temperatures and pressures, certain drilling fluids and or chemicals, and contaminants or debris in the wellbore or drilling fluids.
Apparatus utilizing one or both of these principles is described in U.S. Pat. No 5,165,438 to David M. Facteau. Two fluidic oscillators are achieved by employing wedge-shaped splitters to route the flow of a fluid down diverging diffuser legs. The oscillators connect to a source of fluid flow, provide a mechanism for oscillating the fluid flow between two different locations within the oscillator, and emit fluid pulses downstream of the source of the fluid flow. In one vibrator, a feedback passageway from each leg is routed back to the flow path upstream of the splitter to create a condition establishing oscillating flow through the legs. In a second vibrator, a passageway between the legs downstream of the upstream end of the splitter creates a condition establishing oscillating flow through the legs. A disadvantage of this kind of oscillator is that the diverging diffuser legs required to establish oscillation are expensive to fabricate and prone to clogging from debris in the fluid because of the relative incline between the leg and the axial of the pipe string.
Consequently, there is a need to provide an even more effective fluid oscillator for drill or milling bits which is reliable, long-lived and economical.